Which of the following is a biological agent example?

Viruses are classified as biological agents because they are living organisms that can replicate and cause disease in their hosts, which can be humans, animals, or plants. Unlike chemical agents—such as alcohol—which can affect biological systems but do not reproduce or evolve on their own, viruses are capable of infecting host cells, hijacking their machinery to replicate, and often leading to illness.

Radiation is a physical agent that may cause damage to biological tissues but does not originate from living organisms. Trauma is also not a biological agent; it refers to physical injury rather than an infectious or live agent. Therefore, in the context of identifying biological agents, viruses are the correct choice as they meet the criteria of being living pathogens that can lead to disease outbreaks.